Powerplants for airborne vehicles, such as the propulsion system for an aircraft, use a propulsion system assembly which includes an engine disposed in a nacelle. The engine is mounted to the wing of an aircraft by a pylon or similar support structure for subsonic transports. A channel region is formed adjacent the fuselage of the aircraft. The channel region is bounded by a side surface of the fuselage, a wing lower surface between the fuselage and the pylon, an inboard pylon surface and the nacelle.
Typically, the wings of aircraft with engines mounted in the above manner are swept backwards. The wing extends away from the aircraft from the fuselage to the wing tip in the spanwise direction and rearwardly from the front of the wing to the rear of the wing in the chordwise direction. As a result of a combination of effects related to this wing design and fuselage location, airflow tends to flow from the wing's leading edge and spread in the spanwise direction outwardly away from the aircraft fuselage, rather than flowing rearwardly in the chordwise direction.
A portion of the airflow enters the channel region. At relatively high subsonic Mach numbers, which is likely to occur at cruising speeds, this flow in the channel region may become supersonic. As a result, adverse interference drag effects may occur such as shock wave formation and flow separation from the channel surfaces.
In the past structure was added or contoured to manipulate the airflow to reduce aerodynamic losses. For example, U.S. Pat. No.: 4,314,681 to Kutney entitled Drag-Reducing Component, describes one past attempt to reduce aerodynamic drag caused by ambient air achieving supersonic velocities in the channel region. In Kutney, a tapered bump is inserted at the inboard intersection between the wing and the pylon or a broadly curved outward fairing is mounted on the pylon's inboard surface.
Another approach is to alter the pylon cross section to form a compression pylon as disclosed in U.S. Pat. No.: 4,867,394 to Patterson, Junior entitled Compression Pylon. In this method, the chord length of the pylon is greater than the local chord length of the wing to which it is attached. The cross-sectional area of the pylon progressively increases longitudinally from its leading edge to the local trailing edge of the wing, with the inboard surface of the pylon increasing in distance from the centerline of the pylon. The maximum thickness of the pylon occurs at a point corresponding to the local trailing edge of the wing.
Yet another approach is to camber the pylon as disclosed in U.S. Pat. No.: 4,637,573 to Perin, et alia entitled Arrowlike Aircraft Wing Equipped with a Highlift System and with a Pylon for Suspending the Engine. In this method, the upper part of the pylon adjacent to the leading edge of the wing is bent longitudinally inwardly in the front to rear direction toward the longitudinal axis of the aircraft. Other designs are shown in A1AA 90-2015 paper entitled Design and Analysis of a Large-Plug Inlet ADP Nacelle and Pylon. This paper mentions cambering a portion of the pylon along a circular arc from the nacelle to the wing and was authored by co-inventor Karalus (A. L. Steiner).
The above art notwithstanding, scientists and engineers working under the direction of Applicant's Assignee are still seeking to improve aircraft aerodynamic performance. Accordingly, interest continues in developing an aircraft having a pylon shaped such that previously encountered adverse drag effects in the channel region are reduced.